The relationship between the main gear, the CG and the centre of lift is important for a smooth transfer of weight between wheels and wings at takeoff and landing.
If the main wheels are too far behind the centre of lift the aircraft will tend to over rotate on takeoff and thump the nosewheel down on landing. The change in arms between the tail, the CG and where the weight is being supported (wings or wheels) results in a change in elevator input required as the AOA changes.
So the gear geometry is mainly dictated by how you want the aircraft to respond as you raise or lower the nose on the runway. A tendency to sit on it's tail is more due to a longer fuselage allowing you to load significant weight behind the main gear - a problem that isn't always confined to small aircraft.